Project Summary/Abstract Mental health receives far less attention than physical health with respect to the effects of insurance coverage on access to services and health outcomes. Given the emphasis on improving mental health through prevention and access to quality mental health services, recent expansions of public and commercial health insurance present an opportunity to improve the mental health in the population. Lack of health insurance is recognized as a barrier to effective treatment of mental health disorders. Mental disorders are among the leading causes of disability in the US and there is a well-established connection between mental health and physical health. A key aspect of the recent insurance expansions is the fact that private health insurance policies are mandated to include mental health and substance abuse disorder services. In addition, the Medicaid program was expanded to include individuals with incomes up to 138% of the Federal Poverty Level and commercial insurance has been subsidized to encourage take-up. Commercial insurers also cannot deny coverage based on pre-existing conditions and are restricted in charging higher premiums by age. Such changes at the national-level provide a unique and unprecedented opportunity to study the effects of insurance expansions and mandates on mental health outcomes as well as utilization and out-of-pocket spending for mental health services. Previous studies that have contributed to this topic have typically suffered from confounding that detracts from the ability to understand the causal effects of insurance rather than differences in socioeconomic or demographic traits. Early evidence finds that the insurance expansions increased coverage dramatically and resulted in improved financial outcomes in the targeted population, thus providing further impetus to study possible mental health effects. The proposed study will identify the impacts of the Medicaid and commercial insurance expansions on multiple measures of mental health, encompassing a broad spectrum of potential mental health effects. Moreover, this study will offer unique insight into the mechanisms through which health insurance may affect mental health, investigating numerous measures of health services utilization, prescription drug utilization, and total and out-of-pocket spending. Further, our work will also focus on the effects for the group that is living with mental disorders or is at high-risk of developing such disorders, offering key insight into the distributional effects of the changes in insurance rules, including mandated mental health services. This study is highly innovative as it takes advantage of a nationwide expansion of coverage and differences in implementation by state, offering a natural experiment that can contribute important knowledge about the effects of insurance coverage on the mental health status of the population. We will use a nationally representative dataset to accomplish the proposed Specific Aims.